One of the key technologies in telecommunications is the use of wavelength division multiplexed (WDM) networks to increase bandwidth and efficiency. Depending on the application requirements, various types of grating-based spectrometers and Fourier Transform spectrometers are available for identifying the spectrum of an input light signal and determining spectral lines of interest for an input light signal.
A grating-based spectrometer usually includes bulk optics and an interface to a processing unit. These grating-based spectrometers require complicated fabrication processes to form the gratings as well as careful handling and precise assembly of the bulk optics components. They achieve high resolution by reducing the width of the input aperture, which leads to a reduction in the light gathering capability (étendue) of the device. This results in a low signal to noise ratio (SNR) and high acquisition time. Further, there are physical limits to the resolution based on the density of facets. This ultimately sets a practical limit on resolution regardless of the reduction in étendue.
Another grating-based technology is Array Waveguide Gratings (AWG) technology. AWG technology disperses the spectrum of the input signal based on interference of the input signal caused by a large number of waveguides with a constant length increment. AWG technology can multiplex several wavelengths onto a single physical channel at the transmission end and are also used as demultiplexers at the receiving end of an optical communication network. However, like other grating-based spectrometers, they suffer from limited resolution and require demanding alignment tolerances to function properly.
Fourier Transform Spectrometers (FTS) can deliver high resolution levels comparable to grating-based spectrometers while maintaining a large étendue. However, they usually require moving parts or bulk optics, which are undesirable in a micro-spectrometer.
Finally, planar waveguide wavelength dispersive device technology provides for an arrayed waveguide spectrometer with multiple input apertures to increase étendue.